Two master stations, located on either coast, collect data from the
reference stations to create a GPS correction message. This message
is then broadcast through two geostationary satellites that are in a
fixed position over the equator. The GPS receiver applies the
correction factors contained in the correction message to increase
the accuracy of its measurements.
Note that the signals from the WAAS satellites may not be available
to gauge users in locations where trees, mountains, and other large
objects obstruct the view of the horizon. On other occasions, the
GPS receiver may not be able to access the signals from the three
satellites required to determine a position. As noted earlier, the
gauge stores location information with the results of each
measurement. The measurement display also denotes the quality of
the location fix as follows:
If WAAS information is available during a gauge measurement,
the latitude and longitude will be displayed to the nearest
hundredth (1/100) of a second.
If a GPS location is determined, but the WAAS information is
unavailable, the latitude and longitude will be displayed to the
nearest tenth (1/10) of a second.
If the GPS receiver cannot determine a location, the latitude and
longitude will be denoted as 0.
NOTE
The Wide Area Augmentation System (WAAS) is
currently functional only in the United States.
NOTE
If a Model 3440 Plus equipped with the GPS option is
moved a long distance between uses, the GPS system
must be allowed to initialize. In some instances,
initialization may take as long as 30 to 45 minutes from
the time the gauge is powered on with the GPS enabled.
Note also that the gauge must be positioned such that
the GPS receiver can receive signals from the GPS
satellites as described above. If the GPS does not
initialize within 45 minutes, contact your Troxler
representative.
Model 3430 Plus & 3440 Plus Appendix I–3
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